Add set_attributes_req

`set_attributes_req` is a companion array to `set_attributes` that stores the number of items that need to be worn for the corresponding property list to be active

Example json output:
```
"set_attributes":[[{"id":43,"name":"Cold Resist +{0}%","values":[40]}]],"set_attributes_req":[3]
```

which means that set_attributes[0] requires >= 3 items (set_attributes_req[0] is 3) of the set to be worn to recieve those bonuses

Addresses nokka#5

d2s.go

@@ -588,8 +588,9 @@ func parseItemList(bfr io.ByteReader, itemCount int) ([]item, error) {
 
 			// If the item is part of a set, these bit will tell us how many lists
 			// of magical properties follow the one regular magical property list.
+			var setListValue uint64 = 0
 			if parsed.Quality == partOfSet {
-				setListValue := reverseBits(ibr.ReadBits64(5, true), 5)
+				setListValue = reverseBits(ibr.ReadBits64(5, true), 5)
 				readBits += 5
 
 				listCount, ok := setListMap[setListValue]
@@ -623,6 +624,16 @@ func parseItemList(bfr io.ByteReader, itemCount int) ([]item, error) {
 
 					parsed.SetAttributes = append(parsed.SetAttributes, setAttrList)
 				}
+				// The bits set in setListValue correspond to the number
+				// of items that need to be worn for each list of magical properties
+				// to be active
+				for i := 0; i < 5; i++ {
+					if (setListValue & (1 << uint(i)) == 0) {
+						continue
+					}
+					// bit position 0 means it requires >= 2 items worn, etc
+					parsed.SetAttributesReq = append(parsed.SetAttributesReq, uint(i+2))
+				}
 			}
 
 			if parsed.GivenRuneword == 1 {

item.go

@@ -45,6 +45,7 @@ type item struct {
 	SetName            string             `json:"set_name,omitempty"`
 	SetListCount       uint64             `json:"set_list_count"`
 	SetAttributes      [][]magicAttribute `json:"set_attributes"`
+	SetAttributesReq   []uint             `json:"set_attributes_req,omitempty"`
 	RareName           string             `json:"rare_name,omitempty"`
 	RareName2          string             `json:"rare_name2,omitempty"`
 	MagicalNameIDs     []uint64           `json:"magical_name_ids,omitempty"`